diff mbox series

[2/2] lib/bitmap: drop optimization of bitmap_{from,to}_arr64

Message ID 20230227214524.914050-2-yury.norov@gmail.com
State New
Headers
Series [1/2] lib/test_bitmap: increment failure counter properly |

Commit Message

Yury Norov Feb. 27, 2023, 9:45 p.m. UTC 
  bitmap_{from,to}_arr64() optimization is overly optimistic on 32-bit LE
architectures when it's wired to bitmap_copy_clear_tail().

bitmap_copy_clear_tail() takes care of unused bits in the bitmap up to
the next word boundary. But on 32-bit machines when copying bits from
bitmap to array of 64-bit words, it's expected that the unused part of
a recipient array must be cleared up to 64-bit boundary, so the last 4
bytes may stay untouched when nbits % 64 <= 32.

While the copying part of the optimization works correct, that clear-tail
trick makes corresponding tests reasonably fail:

test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001)

Fix it by removing bitmap_{from,to}_arr64() optimization for 32-bit LE
arches.

Reported-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/lkml/20230225184702.GA3587246@roeck-us.net/
Fixes: 0a97953fd221 ("lib: add bitmap_{from,to}_arr64")
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
---
 include/linux/bitmap.h | 8 +++-----
 lib/bitmap.c           | 2 +-
 2 files changed, 4 insertions(+), 6 deletions(-)

Comments

Alexander Lobakin Feb. 28, 2023, 10:45 a.m. UTC | #1 
From: Yury Norov <yury.norov@gmail.com>
Date: Mon, 27 Feb 2023 13:45:24 -0800

> bitmap_{from,to}_arr64() optimization is overly optimistic on 32-bit LE
> architectures when it's wired to bitmap_copy_clear_tail().
> 
> bitmap_copy_clear_tail() takes care of unused bits in the bitmap up to
> the next word boundary. But on 32-bit machines when copying bits from
> bitmap to array of 64-bit words, it's expected that the unused part of
> a recipient array must be cleared up to 64-bit boundary, so the last 4
> bytes may stay untouched when nbits % 64 <= 32.
> 
> While the copying part of the optimization works correct, that clear-tail
> trick makes corresponding tests reasonably fail:
> 
> test_bitmap: bitmap_to_arr64(nbits == 1): tail is not safely cleared: 0xa5a5a5a500000001 (must be 0x0000000000000001)
> 
> Fix it by removing bitmap_{from,to}_arr64() optimization for 32-bit LE
> arches.
> 
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Link: https://lore.kernel.org/lkml/20230225184702.GA3587246@roeck-us.net/
> Fixes: 0a97953fd221 ("lib: add bitmap_{from,to}_arr64")
> Signed-off-by: Yury Norov <yury.norov@gmail.com>
> Tested-by: Guenter Roeck <linux@roeck-us.net>
> ---
>  include/linux/bitmap.h | 8 +++-----
>  lib/bitmap.c           | 2 +-
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
> index 40e53a2ecc0d..7d4c90eb3df4 100644
> --- a/include/linux/bitmap.h
> +++ b/include/linux/bitmap.h
> @@ -302,12 +302,10 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap,
>  #endif
>  
>  /*
> - * On 64-bit systems bitmaps are represented as u64 arrays internally. On LE32
> - * machines the order of hi and lo parts of numbers match the bitmap structure.
> - * In both cases conversion is not needed when copying data from/to arrays of
> - * u64.
> + * On 64-bit systems bitmaps are represented as u64 arrays internally. So,
> + * the conversion is not needed when copying data from/to arrays of u64.
>   */
> -#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
> +#if BITS_PER_LONG == 32
>  void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits);
>  void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits);
>  #else
> diff --git a/lib/bitmap.c b/lib/bitmap.c
> index 1c81413c51f8..ddb31015e38a 100644
> --- a/lib/bitmap.c
> +++ b/lib/bitmap.c
> @@ -1495,7 +1495,7 @@ void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits)
>  EXPORT_SYMBOL(bitmap_to_arr32);
>  #endif
>  
> -#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
> +#if BITS_PER_LONG == 32
>  /**
>   * bitmap_from_arr64 - copy the contents of u64 array of bits to bitmap
>   *	@bitmap: array of unsigned longs, the destination bitmap

For the series:

Reviewed-by: Alexander Lobakin <aleksander.lobakin@intel.com>

Thanks,
Olek
diff mbox series

Patch

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 40e53a2ecc0d..7d4c90eb3df4 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -302,12 +302,10 @@  void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap,
 #endif
 
 /*
- * On 64-bit systems bitmaps are represented as u64 arrays internally. On LE32
- * machines the order of hi and lo parts of numbers match the bitmap structure.
- * In both cases conversion is not needed when copying data from/to arrays of
- * u64.
+ * On 64-bit systems bitmaps are represented as u64 arrays internally. So,
+ * the conversion is not needed when copying data from/to arrays of u64.
  */
-#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
+#if BITS_PER_LONG == 32
 void bitmap_from_arr64(unsigned long *bitmap, const u64 *buf, unsigned int nbits);
 void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits);
 #else
diff --git a/lib/bitmap.c b/lib/bitmap.c
index 1c81413c51f8..ddb31015e38a 100644
--- a/lib/bitmap.c
+++ b/lib/bitmap.c
@@ -1495,7 +1495,7 @@  void bitmap_to_arr32(u32 *buf, const unsigned long *bitmap, unsigned int nbits)
 EXPORT_SYMBOL(bitmap_to_arr32);
 #endif
 
-#if (BITS_PER_LONG == 32) && defined(__BIG_ENDIAN)
+#if BITS_PER_LONG == 32
 /**
  * bitmap_from_arr64 - copy the contents of u64 array of bits to bitmap
  *	@bitmap: array of unsigned longs, the destination bitmap